<?php

require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/linearBestFitClass.php';
require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/logarithmicBestFitClass.php';
require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/exponentialBestFitClass.php';
require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/powerBestFitClass.php';
require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/polynomialBestFitClass.php';


class trendClass
{
    const TREND_LINEAR                = 'Linear';
    const TREND_LOGARITHMIC            = 'Logarithmic';
    const TREND_EXPONENTIAL            = 'Exponential';
    const TREND_POWER                = 'Power';
    const TREND_POLYNOMIAL_2        = 'Polynomial_2';
    const TREND_POLYNOMIAL_3        = 'Polynomial_3';
    const TREND_POLYNOMIAL_4        = 'Polynomial_4';
    const TREND_POLYNOMIAL_5        = 'Polynomial_5';
    const TREND_POLYNOMIAL_6        = 'Polynomial_6';
    const TREND_BEST_FIT            = 'Bestfit';
    const TREND_BEST_FIT_NO_POLY    = 'Bestfit_no_Polynomials';

    private static $_trendTypes = array( self::TREND_LINEAR,
                                         self::TREND_LOGARITHMIC,
                                         self::TREND_EXPONENTIAL,
                                         self::TREND_POWER
                                       );
    private static $_trendTypePolyOrders = array( self::TREND_POLYNOMIAL_2,
                                                  self::TREND_POLYNOMIAL_3,
                                                  self::TREND_POLYNOMIAL_4,
                                                  self::TREND_POLYNOMIAL_5,
                                                  self::TREND_POLYNOMIAL_6
                                                );

    private static $_trendCache = array();


    public static function calculate($trendType=self::TREND_BEST_FIT, $yValues, $xValues=array(), $const=True) {
        //    Calculate number of points in each dataset
        $nY = count($yValues);
        $nX = count($xValues);

        //    Define X Values if necessary
        if ($nX == 0) {
            $xValues = range(1,$nY);
            $nX = $nY;
        } elseif ($nY != $nX) {
            //    Ensure both arrays of points are the same size
            trigger_error("trend(): Number of elements in coordinate arrays do not match.", E_USER_ERROR);
        }

        $key = md5($trendType.$const.serialize($yValues).serialize($xValues));
        //    Determine which trend method has been requested
        switch ($trendType) {
            //    Instantiate and return the class for the requested trend method
            case self::TREND_LINEAR :
            case self::TREND_LOGARITHMIC :
            case self::TREND_EXPONENTIAL :
            case self::TREND_POWER :
                if (!isset(self::$_trendCache[$key])) {
                    $className = 'PHPExcel_'.$trendType.'_Best_Fit';
                    self::$_trendCache[$key] = new $className($yValues,$xValues,$const);
                }
                return self::$_trendCache[$key];
                break;
            case self::TREND_POLYNOMIAL_2    :
            case self::TREND_POLYNOMIAL_3    :
            case self::TREND_POLYNOMIAL_4    :
            case self::TREND_POLYNOMIAL_5    :
            case self::TREND_POLYNOMIAL_6    :
                if (!isset(self::$_trendCache[$key])) {
                    $order = substr($trendType,-1);
                    self::$_trendCache[$key] = new PHPExcel_Polynomial_Best_Fit($order,$yValues,$xValues,$const);
                }
                return self::$_trendCache[$key];
                break;
            case self::TREND_BEST_FIT            :
            case self::TREND_BEST_FIT_NO_POLY    :
                //    If the request is to determine the best fit regression, then we test each trend line in turn
                //    Start by generating an instance of each available trend method
                foreach(self::$_trendTypes as $trendMethod) {
                    $className = 'PHPExcel_'.$trendMethod.'BestFit';
                    $bestFit[$trendMethod] = new $className($yValues,$xValues,$const);
                    $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                }
                if ($trendType != self::TREND_BEST_FIT_NO_POLY) {
                    foreach(self::$_trendTypePolyOrders as $trendMethod) {
                        $order = substr($trendMethod,-1);
                        $bestFit[$trendMethod] = new PHPExcel_Polynomial_Best_Fit($order,$yValues,$xValues,$const);
                        if ($bestFit[$trendMethod]->getError()) {
                            unset($bestFit[$trendMethod]);
                        } else {
                            $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                        }
                    }
                }
                //    Determine which of our trend lines is the best fit, and then we return the instance of that trend class
                arsort($bestFitValue);
                $bestFitType = key($bestFitValue);
                return $bestFit[$bestFitType];
                break;
            default    :
                return false;
        }
    }    //    function calculate()

}    //    class trendClass